Liquid chromatography is an important branch of analytical chemistry. Recent advances to increase the efficiency and speed of separations performed using liquid chromatography have centered on reducing particle size of the chromatographic packing, reducing column diameter and using open tubular columns analogous to capillary gas chromatography. Open tubular capillary liquid chromatography is a technique that potentially can yield much better efficiency and speed than conventional technology. In order to exploit the advantages of open tubular capillary liquid chromatography, specialized instrumentation and techniques must be used. Yang, U.S. Pat. No. 4,375,163, disclosed on-column detection liquid chromatography with externally coated fused silica capillary columns wherein a segment of the external coating is removed at the end of the column to expose the underlying fused silica and this segment is then positioned in the optical path of a photometric detector. An optical slit is aligned with the longitudinal axis of the column and its use significantly increases the signal to noise ratio associated with detection because the light passes only through the center of the column and is not defracted by the sides of the column. Yang's advance was a major one and much research has been published by others who use this approach. Most workers, including Yang, report using the Jasco Incorporated UVIDEC flow cell holder, adapting it for on-column detection according to Yang, by threading the capillary column on the flow cell holder and then clamping the column in place in front of the slit of the flow cell holder. A problem with the Jasco Incorporated flow cell holder so adapted for on-column detection arises because the column must be bent through four right angles to fit in place on the holder and can break where the external coating has been removed, i.e., the column is quite fragile where the coating has been removed. Another problem with the Jasco Incorporated flow cell holder is that each time a column is fitted thereto, the column must be carefully aligned in front of the slit and then clamped in place without disturbing the alignment.
Spino et al., Journal of Liquid Chromatography, 1987, pages 1603-1611, disclosed a flow cell having a body shaped to be held in a photometric detector. A section of externally coated fused silica capillary tubing with a segment of the coating removed is laid on the body transverse to a passageway through the body. A pair of straight edges (razor blades) are carefully positioned along the segment to form an optical slit. The tube and razor blades are permanently held to the body with glue. The flow cell of Spino was not used for on-column detection and rather the end of the column was connected to the section of tubing glued to the body. If the flow cell of Spino had been used for on-column detection (thus converting it into a column holder), it would have solved the above-mentioned problem of breakage due to the bending of the column but each time a new column was used the old one would have to be demounted from the body, probably breaking or otherwise damaging it, and the slit would have to be carefully reset.
It would be an advance in the art of on-column detection liquid chromatography if a column holder were developed that allowed a capillary column to be easily changed without damaging it and without the necessity of repositioning the slit.